X-ray tube



Z. J. ATLEE May 30, 1944.

X-RAY TUBE Filed June 15, 1942 INVENTORI" Zea J E2766,

Patented May 30,1944

X-RAY TUBE I Zed' J. Atlee, Elmhur'st, Ill., assignor toGene'ral 'Electric X-Ray Corporation, Chicago, 111., a

corporation of New York Application June 15, 1942, Serial N6. 447,030

12'Claims. (or. 250-145 V The present invention relates, in general to electronics and has more particular reference to X-ray generators.

An important object of .the invention is to provide an improved cathode structure protected against the deleterious effects resulting from at a zone orzones exposed to. electronic bombardment.

Another important object is to provide a oath-o ode structure having inserts. of -molybdenum, tungsten or other suitable material highly resistant to disintegration when subjected to electronic bombardment, such inserts being placed in the cathode structure at the surfaces thereof.

whichare apt to be subjected to. electronic bom-.

bardment. Another important obiect is to provide a cathode structure particularly for use in X gray generators having an anode adapted toireceive, with-,

in the area of afocal-spot therein impingement, of electrons emitted by the cathode, wherein,. when operated at high electricalpressure, the anode may become overloaded anditself reach an electron emittingtemperature at the focal spot, thereby constituting the anode-as an electron emitting source capableofprojecting electrons from the focal spot upon facing portions of the cathode structure, the cathode: being-reinforced at its said facing portions-to resist disintegration or other deleteriousefiectsof 1 bombardment by. electrons emitted 'by the-anode; a fur ther object being toeliminate cathode filament failure due-to increased emission thereof caused by destructive effects of electronic bombardment of the cathode structure in the vicinity of the filament; astill further 'object being to minimize metallic deposit on the filament and cn the envelope ofthe generator due to melting of the cathode structure under bombardment, and the resulting failure of the envelope due to such me-- Figure 1 is a sectional view taken through an X-ray tube, embodying the present invention Figure 2 is an enlarged sectional view taken through the anode andcathodecomprising parts of the tube shown in. Figure l;

, Figures. is an end view of the cathode shown in Figure 2; and l 1 I a v Figure 4 is a'sectional view taken substantially along the line 4-4 inIFi'gureB.

To illustrate the invention; the drawing, shows an X-ray generator or tube '|.l comprising spaced anode and cathode electrodes l3 and I5, sealed in an enclosing, preferably glass, envelope [1.

The anode l3 may be'of any suitable or preferred constructionand is suitably mounted in the-envelope l1 and sealed therein at one end or the envelope by a glass-tmmetal seal l9 through which a portion 20 of the anode extends outwardlyof theenvelope to'provide for cooling theanode- I The cathode I,3= likewise is sealed in the envelope, preferably by aglass-to-metal seal 2| at the end-0f the envelope remoteirom the seal l9, said cathode being connected within the envelope toconductors 23 e xtending outwardly of thelenvelope through the seal 2! for the purpose of energizing-the cathode from a suitable source of cathode energizing current outwardly of themvelope. Theanodenand cathode are supported in coaxial spaced apartalignmentin the envelopeand have facing heads. j

It should be understood that X-ray generators function to produce X-rays in responseto the activation of the anode-as an X-ray sourceby impingementonythe head of the-anodeof electrons "emitted by and from the cathode. The cathode head facingthe anode is formed with a cavity or. cup 25 in-Which is disposed an electron emitting filament -2l..- The filament Z'I'is xconnected-withthe conductors-23 and may baconstituted-as an electron emitting element when energized by'the passage therethrough ofcurrent supplied through the conductors 23. By applying ail-electrical potential between the. filament 21 and the facing head of the anode, as by connect-' ingone of the conductors 23 and the outwardly 7 extending portions 20 of the anode with a suit able source of electrical potential, electrons emitted by the filament 21 may be caused .to travel from thefilament as an electron streamifi and impinge upon aportion of the head of theanode forming a target-area 3|. The cup 25 serves to focus the electrons comprising the stream 29 upon the target zone 3 I. l

- It will beznoted thatthe headof the anode reduced thickness opposite the head of the anode, thereby forming an X-ray window 35 in the envelope. During the operation of the X-ray generator a considerable amount of heat is developed in the anode which may be dissipated outwardly of the envelope by radiation from the I anode through the envelope walls and by conduction through the anode and its outwardly extending portion 20. .f

If the generator, as frequently happens when operated as a self-rectified diagnostic tube, is overloaded, the focal spot 3| may, and frequently does, reach a temperature at which the focal spot itself becomes an electron emitting source of electrons which may pass thence as a secondary beam of electrons 31 focused upon a portion of the cathode structure.

The establishment of such a secondary beam of electrons impinging upon a portion of the cathode structure may result in destructive bombardment of the portions of the cathode structure upon which impinge the electrons comprising such beam. Where the cathode head comprises ironor nickel, which'are the metals usually employed in making cathode heads, such electronic impingement may. cause disintegration of the head by melting thereof at the place of impingement. Electronic bombardment of the cathode head, tends to raise the temperature thereof and. of the filament 21, mounted thereon, thereby tending to cause failure of the filament as a result of increased electron emission therefrom. Melting of the cathode head metal under secondary bombardment of the character described results in thesputtering of the melted material upon the'electrodes and upon the surrounding walls of the envelope. Excessive me tallic deposits on the envelope may cause the same to fail,,whi1e metallic deposit upon the electrodes tends to impair the operating efiiciency thereofja nd to cause filament failure. In order to overcome the deleterious efiects of electron bombardment of the cathode head, the head is reinforced and protected atthe portions thereof which are apt to be subjected to electronic bombardment. This is accomplished by applying 'to'said portions an insert 39 comprising material-such" as'molybdenum or tungsten having theability'to resist melting under electronic bombardment. The insert 39, as shown more particularly in Figures 3 and 4, comprises a plug ofmaterialset into the face of the cathode head at the zone thereof which faces the anode focal spot 3|, the plug, in the illustrated embodiment, being disposed in the'head in position lying in the path of such electrons as may emanate at right angles from the anode focal spot 3|. The plug extends in the cathode cup at oneend thereof, said cup, in the embodiment shown. being of elongated configuration to, receive the elongated filament 21.' The plug may be secured to the head and integrated therewith as by brazing or by any other uitable joining process, to form .an electron receiving shield on the cathode head to protect the same against destructive effects of electron bombardment.

It is thought that the invention and its numerous attendant advantages will be fully derstood from the foregoing description-and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit or scope .of the invention, or sacrificing any of its attendant advantages, the form herein disclosed being a preferred embodiment for the purpose of illustrating the invention.

The invention is hereby claimed as follows:

1. In a deviceof the class described, an anode and a cooperating cathode comprising a head and an electron emitting source carried on said head in position to emit electrons for impingement upon said anode at a target zone therein,

said cathode head having inserted portions comprising tungsten and characterized by resistance' to disintegration under electronic bombardment at high temperature, said portion being disposed in position to receive impingement of electrons emitted by said anode.

3. In a device of the class described, an anode and a cooperating cathode comprising a head' and an electron emitting source carried on said head in position to emit electrons for impingement upon said anodeat a target zone therein, said cathode head having inserted portions comprising molybdenum and characterized by resistance to disintegration under electronic bombardment at high temperature, said portionbeing disposed in position to receive impingement of electrons emitted by said anode.

4.. In a device of the class described, an anode and a cooperating cathode comprising a head and an electronemitting source carried on said head in position to emit electrons for impingement upon said anode at a target zone therein, said cathode head comprising metal such as iron or nickel and having inserts of material having a melting temperature higher than that of iron or nickel and characterized by resistance to disintegration under electronic bombardment at high temperature, said inserts being disposed in position to receive impingement of electron emitted by said anode, v i

5. In a device of the class described, an anode and a cooperating cathode comprising a head and an electron emitting source carried on said head in position to emit electrons for impingement upon said anode at a target zone therein, said cathode head comprising metal such as iron Or nickel and having inserts of tungsten characterized by resistance to disintegration under electronic bombardment at high temperature and being disposed in position to receive impingement of electrons emitted by said anode.

der electronic bombardment at high temperature and being disposed in position to receive impingement of electrons emitted by said anode.

'7. A cathode comprising a head of material subject to disintegration when electronically bombarded and an insert of material highly resistant to disintegration under electron bombardment carried on said head in position to intercept electrons emitted from a predetermined source whereby to protect the head against disintegration by electronic bombardment from said source.

8. A cathode comprising a head of material subject to disintegration when electronically bombarded and an insert of tungsten carried on said head in position to intercept electrons emitted from a predetermined source whereby to protect the head against disintegration by electronic bombardment from said source.

9. A cathode comprising a head of material subject to disintegration when electronically bombarded and an insert of molybdenum carried on said head in position to intercept electrons emitted from a predetermined source whereby to protect the head against disintegration by electronic bombardment from said source.

10. A cathode comprising a head of material readily fusible under electronic bombardment and an insert on said head at an area thereof subject to bombardment, said insert comprising material having a high melting temperature and adapted to receive electrons emitted from a predetermined source and protect said head against disintegration by electrons emitted from said source.

11. A cathode comprising a head of material readily fusible under electronic bombardment and an insert on said head at an area thereof subject to bombardment, said insert comprising tungsten adapted to receive electrons emitted from a predetermined source and protect said head against disintegration by electrons emitted from said source.

12. A cathode comprising a head of material readily fusible under electronic bombardment and an insert on said head at an area thereof subject to bombardment, said insert comprising molybdenum adapted to receive electrons emitted from a predetermined source and protect said head against disintegration by electrons emitted from said source.

ZED J. ATLE'E. 

